You know, cosine is adjacent over hypotenuse.

你们知道 cos是邻边除以斜边。

That's the cosine of 30 degrees.

这是cos30度。

So the factor by which the slice gets squished down in this direction is exactly cosine of theta.

因，切片 在这个方向上被压扁的因素正是 theta 的余弦。

But let me go back to these sines, cosines and logarithms.

但让我们再来说说正弦、余弦和对数函数。

What's the cosine of 30 degrees?

cos30度是多少？

And compute over 10,000 calculations by cosine, square root and lately Analytic Geometry.

还要完成上万笔计算处余弦，平方根，最近还用起了解析几何。

98 times the cosine of 30 degrees newtons.

98乘以 cos 30度牛顿。

And that's why it's cosine of theta.

因 相等。

Because cosine of 0 right now is 1.

因 相等。

So this is equal to cosine of the angle.

cosθ等于邻边/斜边。

Here I'm only showing cosines for simplicity.

在这里， 为了简单起见，我只显示余弦。

How is knowing cosines gonna help you with your backstroke?

学会余弦对仰泳有什么帮助？

So, the cosine of theta is equal to the (ball’s position) divided by its (amplitude).

因， theta 的余弦等于（球的位置）除以它的（振幅）。

I don't have the slightest idea what sine and cosine mean.

我根本不知道正弦和余弦是什么意思。

In other words, the ball’s position is equal to (the amplitude), times (the cosine of the angle).

换句话说， 球的位置等于（振幅）乘以（角度的余弦值）。

So, the law of cosines is an extension of the pythagorean theorem to the arbitrary angles...

所以余弦定律是勾股定对任意角度的延伸。

So, the cosine of theta is equal to the (ball's position) divided by its (amplitude).

所以theta的答案等于位置 球除以幅度。

So we know that T1 cosine of 30 is going to equal T2 cosine of 60.

所以我们知道T1cos30°应该等於T2cos60°我们把这写下来。

And then I need to multiply by cosine of the angle in this case the angle is 30 degrees.

然后我需要乘以角度的余弦，在这种情况下角度是 30 度。

Well, it's going to be the tension in the first wire, 200 Newtons times the cosine of 30 degrees.

好吧，这将是第一根电线的张力，200 牛顿乘以 30 度的余弦。